Reinforced tread and method of forming

ABSTRACT

A method for forming a composite tread, the method comprising the steps of forming a coextruded strip of a first compound and a second compound, wherein the first compound is a tread compound, and the second compound is formed from a high-wear compound, wherein the tread is formed from winding the coextruded strip onto the tire building drum while varying the ratio of the first compound to the second compound.

FIELD OF THE INVENTION

The invention relates in general to tire manufacturing, and moreparticularly to a method for forming a reinforced composite tread.

BACKGROUND OF THE INVENTION

Tire manufacturers have progressed to more complicated designs due to anadvance in technology as well as a highly competitive industrialenvironment. In particular, tire designers seek to use multiple rubbercompounds in a tire component such as the tread in order to meetcustomer demands. Using multiple rubber compounds per tire component canresult in a huge number of compounds needed to be on hand for thevarious tire lines of the manufacturer. For cost and efficiency reasons,tire manufacturers seek to limit the number of compounds available, dueto the extensive costs associated with each compound. Each compoundtypically requires the use of a banbury mixer, which involves expensivecapital expenditures. Furthermore, banbury mixers have difficulty mixingup tough or stiff rubber compounds. The compounds generated from thebanbury mixers are typically shipped to the tire building plants, thusrequiring additional costs for transportation. The shelf life of thecompounds is finite, and if not used within a certain time period, isscrapped.

Thus, it is desired to have an improved method and apparatus whichprovides independent flow of two or more compounds from a singleapplication head, and allows the ratio of the two different compounds tobe varied instantaneously. More particularly, it is desired to be ableto make a custom tire tread directly onto a tire building machine in anefficient manner, reducing the need for multiple stations. This methodcan be used to make treads with the focus of improving characteristicssuch as rolling resistance, wet traction, and durability. One such treadis a reinforced tread.

Definitions

“Aspect Ratio” means the ratio of a tire's section height to its sectionwidth.

“Axial” and “axially” means the lines or directions that are parallel tothe axis of rotation of the tire.

“Bead” or “Bead Core” means generally that part of the tire comprisingan annular tensile member, the radially inner beads are associated withholding the tire to the rim being wrapped by ply cords and shaped, withor without other reinforcement elements such as flippers, chippers,apexes or fillers, toe guards and chafers.

“Belt Structure” or “Reinforcing Belts” means at least two annularlayers or plies of parallel cords, woven or unwoven, underlying thetread, unanchored to the bead, and having both left and right cordangles in the range from 17° to 27° with respect to the equatorial planeof the tire.

“Bias Ply Tire” means that the reinforcing cords in the carcass plyextend diagonally across the tire from bead-to-bead at about 25-65°angle with respect to the equatorial plane of the tire, the ply cordsrunning at opposite angles in alternate layers.

“Breakers” or “Tire Breakers” means the same as belt or belt structureor reinforcement belts.

“Carcass” means a laminate of tire ply material and other tirecomponents cut to length suitable for splicing, or already spliced, intoa cylindrical or toroidal shape. Additional components may be added tothe carcass prior to its being vulcanized to create the molded tire.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection; it can also refer to the direction of the sets of adjacentcircular curves whose radii define the axial curvature of the tread asviewed in cross section.

“Cord” means one of the reinforcement strands, including fibers, whichare used to reinforce the plies.

“Inner Liner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire.

“Inserts” means the reinforcement typically used to reinforce thesidewalls of runflat-type tires; it also refers to the elastomericinsert that underlies the tread.

“Ply” means a cord-reinforced layer of elastomer-coated, radiallydeployed or otherwise parallel cords.

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire.

“Radial Ply Structure” means the one or more carcass plies or which atleast one ply has reinforcing cords oriented at an angle of between 65°and 90° with respect to the equatorial plane of the tire.

“Radial Ply Tire” means a belted or circumferentially-restrictedpneumatic tire in which the ply cords which extend from bead to bead arelaid at cord angles between 65° and 90° with respect to the equatorialplane of the tire.

“Sidewall” means a portion of a tire between the tread and the bead.

“Tangent delta”, or “tan delta,” is a ratio of the shear loss modulus,also known as G″, to the shear storage modulus (G′). These properties,namely the G′, G″ and tan delta, characterize the viscoelastic responseof a rubber test sample to a tensile deformation at a fixed frequencyand temperature, measured at 100° C.

“Laminate structure” means an unvulcanized structure made of one or morelayers of tire or elastomer components such as the innerliner,sidewalls, and optional ply layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1A is a perspective view of a coextruded strip of two layers,wherein the first layer is formed of a first compound and the secondlayer is formed of a second compound of the present invention, whereinthe ratio of the first compound to the second compound is 90/10; FIG. 1Bis a perspective view of a coextruded strip wherein the first layer is95% of a first compound and the second layer formed of a secondcompound, wherein the ratio of the first compound to the second compoundis 95/5;

FIG. 2 is a cross-sectional view of an encapsulated tire tread of thepresent invention;

FIG. 3 is a front view of an encapsulated tire tread during formationwith strip lamination before vulcanization;

FIG. 4 is a front view of an encapsulated tire tread aftervulcanization;

FIG. 5 is a cross-sectional view of the cured tire with an encapsulatedtread;

FIG. 6 is a second embodiment of an encapsulated tread profile;

FIG. 7 is a close up cross-sectional view of a dual compound apparatusfor forming a coextruded strip onto a tire building drum; and

FIG. 8A is a perspective cutaway view of a coextrusion nozzle of thepresent invention, while FIG. 8B is a side cross-sectional view of thecoextrusion nozzle of FIG. 8A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 illustrates a cross-sectional view of a desired reinforced tiretread profile 200 of the present invention. The tire tread 200 is formedby strip lamination, or by winding a continuous coextruded strip 210onto a tire building drum 18 or a shaped green carcass. The continuousstrip 210 is shown in FIG. 1A, and is a dual layer or coextruded stripof a first layer 212 and second layer 214 of two different rubber treadcompounds. The first and second layers 212,214 are discrete, and notmixed together. The first layer 212 is formed from a first rubbercompound which can be any mono cap tread compound, typically fullsilica. The second compound is preferably a high wear rubber compound,preferably a compound having a very high G′ stiffness. The combinationof the tread compound made with silica and the second compound of veryhigh stiffness results in a tire tread with the desired wet performanceand low rolling resistance, while providing desired stiffness in thedesignated areas of the tread.

The stiffness may be characterized by the dynamic modulus G′, which aresometimes referred to as the “shear storage modulus” or “dynamicmodulus,” reference may be made to Science and Technology of Rubber,second edition, 1994, Academic Press, San Diego, Calif., edited by JamesE. Mark et al, pages 249-254. The shear storage modulus (G′) values areindicative of rubber compound stiffness which can relate to tireperformance. In a first embodiment, the second rubber compound comprisesa stiff rubber composition having a shear storage modulus G′ measured at1% strain and 100° C. according to ASTM D5289 ranging from 15 to 50 MPa.In a more preferred embodiment, the second rubber compound comprises arubber composition having a shear storage modulus G′ measured at 1%strain and 100° C. according to ASTM D5289 ranging from 25 to 40 MPa. Inthe most preferred embodiment, the second rubber compound comprises arubber composition having a shear storage modulus G′ measured at 1%strain and 100° C. according to ASTM D5289 ranging from 30 to 40 MPa.

The first and second rubber compounds of the strip are in discretelayers, and thus are not mixed together. The coextruded strip shown inFIG. 1A has a ratio of 90% of the first compound to 10% of the secondcompound, while FIG. 1B illustrates a ratio of 95% of the first compoundto 5% of the second compound. The invention is not limited to same, andother ratios as desired may be utilized. The apparatus used to form thecontinuous coextruded strip is described in the paragraphs below, and isshown in FIGS. 7-8. The apparatus can form the coextruded strip whileinstantaneously varying the ratio of the first compound to the secondcompound.

The first layer thickness of the first compound is preferably in therange of about 0.3 mm to about 2 mm, and more preferably in the range ofabout 0.6 to about 1.2 mm. The second layer thickness of the secondcompound preferably has a thickness in the range of about 0.01 mm toabout 0.2 mm, more preferably about 0.01 mm to about 0.1 mm. The overallwidth of the strip 210 is in the range of about 10 mm to about 50 mm,more preferably 20-40 mm. The term “about” as used herein means avariation of +/−10%.

The coextruded strip forming apparatus 10 is used to form the treadprofile 200 shown in FIG. 2 by rotating the drum 18 (or carcass) andthen applying a continuous coextruded strip 210 by spirally winding thestrip onto the drum 18 or carcass. The tread lateral ends 220, 222 areformed from the coextruded strip 210 having a volume ratio in the rangeof 90-100% compound A and 0-10% compound B. A coextruded strip is usedto form each lateral end 220,222, wherein the coextruded strip ispreferably 95-100% of the first or desired tread compound and 0-5% ofthe second compound.

Between the lateral ends 220,222 the tread has a base layer 230preferably located radially inward of the tread profile, and extendingbetween the lateral ends 220,222. The base layer 230 is formed from acoextruded strip having a volume ratio preferably in the range of 0-10%first compound, and 90-100% of the stiff second compound or high weartread compound. The base layer is formed by spirally winding thecoextruded strips, and wherein the strips may form the first row byoverlapping the coextruded strips with each other. The volume ratio ofthe first compound to the second compound may be varied over the baselayer. The tread further includes tread blocks 250 which are formed bycoextruded strips having a volume ratio in the range of 90-100% of thefirst read compound and 0-10% of the second high wear compound. Thetread preferably has reinforced circumferential grooves 240 wherein thegroove walls 242 and groove bottom 244 are formed from coextruded stripshaving a volume ratio in the range of 0-10% of the first compound and90-100% high wear or high stiffness compound. There are typically one totwo rows of strips to form the tread blocks by winding the coextrudedstrips.

FIG. 6 illustrates a second embodiment 300 of a desired tread profilehaving an encapsulated tread blocks 350, while FIGS. 3-5 areillustrations of the tire before and after cure. As shown in FIG. 6, thelateral ends 320,322 of the tread is formed from the first compound. Thetread has a radially inner base layer 330 formed primarily of the highwear or highly stiff second compound. The base layer 330 is formed froma coextruded strip having a volume ratio preferably in the range of0-10% first compound, and 90-100% of the stiff second compound or highwear tread compound. The base layer is formed by spirally winding thecoextruded strips, and wherein the strips may form the first row byoverlapping the coextruded strips with each other. The volume ratio ofthe first compound to the second compound may be varied over the highwear layer. The inner portions of the tread blocks 360 are also formedfrom 100% of the first tread compound. Each tread block 360 isencapsulated by an outer layer 370 and inclined walls 380 that areformed of the coextruded strip having a volume ratio in the range of0-10% first compound, and 90-100% of the stiff second compound or highwear tread compound. A groove 340 is formed by the inclined walls 380and groove bottom 344. The groove bottom 344 is also reinforced andformed of the coextruded strip having a volume ratio in the range of0-10% first compound, and 90-100% of the stiff second compound or highwear tread compound. The stiff compound which outlines each groove andtread block together with the stiff inner base layer 230 provides areinforced tread.

Coextruded Strip Forming Apparatus

As shown in FIGS. 7-8, the coextruded strip forming apparatus 10includes a first extruder 30 and a second extruder 60, preferablyarranged in close proximity in a stacked manner. The first extruder 30has an inlet 32 for receiving a first rubber composition A, while thesecond extruder 60 has an inlet 62 for receiving a second rubbercomposition B. Each extruder functions to warm up the rubber compositionto the temperature in the range of about 80° C. to about 150° C.,preferably about 90° C. to about 120° C., and to masticate the rubbercomposition as needed. The coextruded strip forming apparatus 10 ismounted so that it can translate fore and aft in relation to a tirebuilding machine 18.

The first compound is extruded by the first extruder 30 and then pumpedby the first gear pump 42 into a nozzle 100, while at the same time thesecond compound is extruded by the second extruder 60 and then pumped bythe second gear pump 44 into the coextrusion nozzle 100.

The coextrusion nozzle 100 has a removable insert 120 that functions todivide the nozzle into a first and second flow passageway 122,124. Theremovable insert 120 is preferably rectangular in cross-sectional shape.The removable insert 120 has a distal end 130 with tapered ends 132,134forming a nose 136. The nose 136 is positioned adjacent the nozzle dieexit 140 and spaced a few millimeters from the die exit 140. The regionbetween the nose 136 and the die exit 140 is a low volume coextrusionzone 150 that is high pressure. In the low volume coextrusion zone 150,compound A flowstream 122 merges with compound B flowstream 124 formingtwo discrete layers 212,214 joined together at an interface 215.

The volume ratio of the first compound to the second compound may bechanged by varying the ratio of the speed of the first gear pump to thespeed of the second gear pump. The dual coextruded strip formingapparatus 10 can adjust the speed ratios on the fly, and due to thesmall residence time of the coextrusion nozzle, the apparatus has a fastresponse to a change in the compound ratios. This is due to the lowvolume of the coextrusion zone.

In summary the methods and equipment used to form a coextruded strip oftwo different compounds can be used to create a tread reinforcementstructure with the reinforcement compound in targeted areas to provideextra stiffness where it is most effective without replacing largeamounts of the main compound and compromising RR. The tread may also bereinforced in a different way, by increasing the ratio of reinforcementcompound across the rib to create a stiffness gradient, as analternative to a hard change from one compound to the other. This typeof distribution would be impossible with a conventional extruder.

Variations in the present inventions are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed which will be within the full intended scope of the inventionas defined by the following appended claims.

What is claimed is:
 1. A method for forming a composite tread, themethod comprising the steps of: forming a coextruded strip of a firstcompound and a second compound, wherein the first compound is a treadcompound, and the second compound is formed from a high-wear compound,wherein the tread is formed from winding the coextruded strip onto thetire building drum while varying the ratio of the first compound to thesecond compound.
 2. The method of claim 1 wherein at least one of thelateral edges of the tread are 90-100% of the first compound.
 3. Themethod of claim 1 wherein the tread further comprises one or more treadblocks, wherein the tread blocks are formed from winding a coextrudedstrip having a volume ratio of 90-100% of the first compound, and 0-10%of the second compound.
 4. The method of claim 1 wherein the treadblocks have an outer layer formed from a coextruded strip having avolume ratio of 0-10% of the first compound, and 90-100% of the secondcompound.
 5. The method of claim 1 wherein the tread has one or moregrooves, wherein the walls of the grooves are formed from a layer of100% of the second compound.
 6. The method of claim 1 wherein the secondcompound comprises a rubber composition having a shear storage modulusG′ measured at 1% strain and 100° C. according to ASTM D5289 rangingfrom 23 to 31 MPa.
 7. The method of claim 1 wherein the second compoundcomprises a rubber composition having a shear storage modulus G′measured at 1% strain and 100° C. according to ASTM D5289 ranging from23 to 50 MPa.
 8. The method of claim 1 wherein the second compoundcomprises a rubber composition having a shear storage modulus G′measured at 1% strain and 100° C. according to ASTM D5289 ranging from40 to 60 MPa.
 9. The method of claim 1 wherein the ratio of the firstcompound to the second compound is varied by changing the ratio of thespeed of a first gear pump to a second gear pump.
 10. The method ofclaim 1 wherein the strip is formed in a continuous manner.
 11. Themethod of claim 1 wherein the coextruded strip is applied in acontinuous manner to a tire building machine to build a tire component.12. The method of claim 1 wherein the tread has one or more grooves,wherein the walls of the grooves are formed from a layer of thecoextruded strip having a volume ratio of 0-10% of the first compound,and 90-100% of the second compound.
 13. A tire having a tread, whereinthe tread is formed from a continuous spiral winding of a coextrudeddual layer strip of a first and second rubber, wherein the firstcompound is made of silica, and the second compound is selected for highwear, wherein the tread has a first layer formed from spirally winding acontinuous coextruded strip of 90-99% of the second compound and 1-9% ofthe first compound, wherein the lateral edges of the tread and one ormore of the tread blocks are formed of 90-99% of the first compound and1-10% of the second compound, wherein the outline of the lateral edgesand each of the one or more tread blocks are formed in the range of80-100% of the second compound.
 14. The tire tread of claim 13 whereinthe second compound comprises a rubber composition having a shearstorage modulus G′ measured at 1% strain and 100° C. according to ASTMD5289 ranging from 23 to 50 MPa.
 15. The tire tread of claim 13 whereinthe second compound comprises a rubber composition having a shearstorage modulus G′ measured at 1% strain and 100° C. according to ASTMD5289 ranging from 40 to 60 MPa.
 16. The tire tread of claim 13 whereinthe second layer of compound has a thinner gauge than the first layer ofcompound.
 17. The tire tread of claim 13 wherein the continuouscoextruded strip has a rectangular cross-sectional shape.
 18. The tiretread of claim 13 wherein the continuous coextruded strip has atrapezoidal cross-sectional shape.
 19. The tire tread of claim 13wherein the continuous coextruded strip has an ellipticalcross-sectional shape.
 20. The tire tread of claim 13 wherein thelateral edges of the tread are 99% of a first compound.